Relating to treatment of water

ABSTRACT

The present invention relates to water treatment. In one embodiment there is provided a method of treating an aqueous system to inhibit growth of one or more micro-organisms therein and/or to reduce the number of live micro-organisms therein. The method comprises adding treatment agents to said aqueous system and wherein said treatment agents comprise: (a) a phosphonium compound; and (b) an oxazolidine compound.

FIELD OF THE INVENTION

The present invention relates to water treatment, particularly thoughnot exclusively, to methods of treating aqueous systems to inhibitgrowth of micro-organisms.

BACKGROUND TO THE INVENTION

The presence and growth of micro-organisms in aqueous systems,especially in industrial water systems, is a concern. Examples ofindustrial water systems where micro-organisms are a concern includecooling water systems, pulping and papermaking systems and oil and gasfield water systems.

The presence of micro-organisms in industrial water systems may resultin the formation of deposits on system surfaces. These deposits or slimecan give rise to various problems. In cooling water systems, slime mayrestrict water flow, reduce heat transfer efficiency, cause corrosionand may be aesthetically unappealing especially if algae are present dueto their visible green pigmentation. Corrosion can also occur inindustrial water systems in the absence of visible slime through theaction of micro-organisms.

In pulp and paper mill systems, slime formed by micro-organisms maycause fouling, plugging, or corrosion of the system. The slime may alsobreak loose and become entrained in the paper produced causingblemishes, holes, tears, and odour in the finished product. The endresult may therefore be unusable product and wasted output.

Slime can also be a problem in oil and gas field water systems and maycause energy losses due to increased fluid frictional resistance,formation plugging and corrosion. The slime may harbour a mixture ofaerobic and anaerobic bacteria that are responsible for the productionof hydrogen sulfide gas. The hydrogen sulfide may cause souring of oiland gas which may reduce the quality of these products and increasetreatment costs.

Pseudomonas aeruginosa bacteria are commonly present in air, water andsoil. These bacteria continually contaminate open cooling water systems,pulping and papermaking systems and oil and gas field water systems andare among the most common slime formers. Slime may be viewed as being amass of cells stuck together by the cementing action of the gelatinoussecretions around each cell. The slime entraps other debris, restrictswater flow and heat transfer and may serve as a site for corrosion.

Chlorella vulgaris algae are also commonly present in air, water andsoil. These algae continually contaminate open cooling water systems andtheir growth turns the water and surfaces in these systems green. Theyalso provide a food source for bacteria, which can stimulate slimeformation, and protozoa which can harbour the pathogenic bacteriumLegionella pneumophila.

A known method of controlling microbial growth in aqueous systems is touse biocides. While biocides are known to inhibit microbial growth thebiocidal effect is generally of limited duration. The effectiveness ofknown biocides may be rapidly reduced as a result of exposure tonegative influences. Negative influences may include temperature, pH orreaction with ingredients present in the system which neutralizes theirbiocidal effect. Therefore, the use of such biocides may involvecontinuous or frequent addition and their application at multiple sitesor zones in the system to be treated. The cost of the biocide treatmentand the labour costs associated with the application of known biocidesmay therefore be significant.

Known biocides are also highly toxic in the quantities known to berequired for effective control of microbial populations. As a result,the amount of biocides that can be safely discharged into theenvironment may be limited by environmental regulations. Therefore, theneed exists for improved methods for controlling microbial growth inaqueous systems.

As noted above, known biocides have a number of limitations includingthe large quantities of biocides which typically have to be used toachieve the desired biocidal effect and the potential harmful effects onthe environment of biocides and therefore reducing the amount necessaryfor control and thus the quantity released to the environment has manybenefits.

Accordingly, the present invention aims to address at least onedisadvantage associated with the prior art whether discussed herein orotherwise.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method oftreating an aqueous system as set forth in the appended claims. Otherfeatures of the invention will be apparent from the claims, and thedescription which follows.

According to a first aspect of the present invention there is provided amethod of treating an aqueous system to inhibit growth of one or moremicro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to said aqueous system and wherein said treatment agentscomprise:

(a) a phosphonium compound; and(b) an oxazolidine compound.

Suitably, the oxazolidine compound is selected from the group consistingof oxazolidines and oxazolidine derivatives. Suitably, the oxazolidinecompound comprises an oxazolidine. Suitably, the oxazolidine compoundconsists of an oxazolidine. Suitably, the oxazolidine compound comprisesan oxazolidine derivative. Suitably, the oxazolidine compound consistsof an oxazolidine derivative.

Suitably, the oxazolidine compound comprises a methyloxazolidine.Suitably, the oxazolidine compound consists of a methyloxazolidine.Suitably, the oxazolidine compound comprises a dimethyloxazolidine.Suitably, the oxazolidine compound consists of a dimethyloxazolidine.Suitably, the oxazolidine compound comprises 4,4-dimethyloxazolidine(also known as DMO). Suitably, the oxazolidine compound consists of4,4-dimethyloxazolidine.

Suitably, the method comprises adding a phosphonium compound as aphosphonium compound composition. The method may comprise adding aphosphonium composition comprising one or more phosphonium compounds andwater. The method may comprise adding a phosphonium compositioncomprising a single phosphonium compound and water.

Suitably, the method comprises adding an oxazolidine compound as anoxazolidine composition. The method may comprise adding an oxazolidinecomposition comprising an oxazolidine compound and water. The method maycomprise adding an oxazolidine composition comprising one or moreoxazolidine compounds and water. The method may comprise adding anoxazolidine composition comprising a single oxazolidine compound andwater.

The oxazolidine composition may comprise an oxazolidine and water. Theoxazolidine composition may consist of an oxazolidine and water. Theoxazolidine composition may comprise a methyloxazolidine and water. Theoxazolidine composition may consist of a methyloxazolidine and water.The oxazolidine composition may comprise a dimethyloxazolidine andwater. The oxazolidine composition may consist of a dimethyloxazolidineand water. The oxazolidine composition may comprise4,4-dimethyloxazolidine and water. The oxazolidine composition mayconsist of 4,4-dimethyloxazolidine and water. The oxazolidinecomposition may comprise 4,4-dimethyloxazolidine as the sole oxazolidinecompound.

Suitably, the method comprises treating an aqueous system such that4,4-dimethyloxazolidine comprises greater than 50% of the totaloxazolidine compound(s) added to the aqueous system. Suitably, themethod comprises treating an aqueous system such that4,4-dimethyloxazolidine comprises greater than 90% of the totaloxazolidine compound(s) added to the aqueous system, for example 99% orgreater.

Suitably, the method comprises treating an aqueous system such that4,4-dimethyloxazolidine comprises greater than 50% of the totaloxazolidine compound(s) present in the aqueous system. Suitably, themethod comprises treating an aqueous system such that4,4-dimethyloxazolidine comprises greater than 90% of the totaloxazolidine compound(s) present in the aqueous system, for example 99%or greater.

Suitably, the method employs 4,4-dimethyloxazolidine as the onlyoxazolidine compound (b).

Suitably, there is provided a method of treating an aqueous system toinhibit growth of one or more micro-organisms therein and/or to reducethe number of live micro-organisms therein, wherein the method comprisesadding treatment agents to said aqueous system and wherein saidtreatment agents comprise:

(a) a phosphonium compound; and(b) 4,4-dimethyloxazolidine.

Suitably, the method comprises treating an aqueous system to inhibitgrowth of anaerobic bacteria and/or to reduce the number of liveanaerobic bacteria therein. Suitably, the method comprises treating anaqueous system to inhibit growth of facultative anaerobic bacteriaand/or to reduce the number of live facultative anaerobic bacteriatherein. Suitably, the method comprises treating an aqueous system toinhibit growth of aerobic bacteria and/or to reduce the number of liveaerobic bacteria therein.

Suitably the aqueous system comprises a mixture of water and otherconstituents. The aqueous system may contain oil. The aqueous system maycomprise an oil and water emulsion. The aqueous system may comprisesolids. The aqueous system may comprise suspended solids. The aqueoussystem may comprise high levels of dissolved solids. The aqueous systemmay comprise one or more salts, for example sodium chloride. Suitably,the aqueous system consists of a body of water. Suitably, the aqueoussystem consists of a body of water which comprises water and otherconstituents, for example dissolved solids.

Suitably, the aqueous system comprises an industrial water system. Theaqueous system may consist of industrial water. The aqueous system mayconsist of industrial water which may comprise water and otherconstituents. The aqueous system may comprise a cooling water system.The aqueous system may consist of cooling water which may comprise waterand other constituents. The aqueous system may comprise a pulping andpapermaking system. The aqueous system may consist of pulping andpapermaking water which may comprise water and other constituents. Theaqueous system may comprise an oil and gas field water system. Theaqueous system may consist of oil and gas field water which may comprisewater and other constituents. The aqueous system may comprise a welltreatment fluid. The aqueous system may consist of well treatment fluidwhich may comprise water and other constituents.

Suitably, the method comprises treating industrial water to inhibitgrowth of one or more micro-organisms therein and/or to reduce thenumber of live micro-organisms therein, wherein the method comprisesadding treatment agents to said industrial water. The method maycomprise treating cooling water to inhibit growth of one or moremicro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to said cooling water. The method may comprise treating pulpingand papermaking water to inhibit growth of one or more micro-organismstherein and/or to reduce the number of live micro-organisms therein,wherein the method comprises adding treatment agents to said pulping andpapermaking water. The method may comprise treating oil and gas fieldwater to inhibit growth of one or more micro-organisms therein and/or toreduce the number of live micro-organisms therein, wherein the methodcomprises adding treatment agents to said oil and gas field water. Themethod may comprise treating a well treatment fluid to inhibit growth ofone or more micro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to well treatment fluid.

Suitably, the method comprises treating an aqueous system whichcomprises dissolved solids.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 1000 mg l⁻¹ or greater. Suitably, the aqueoussystem has a total dissolved solids (TDS) of at least 2000 mg l⁻¹, forexample at least: 3000 mg l⁻¹; 4000 mg l⁻¹; 5000 mg l⁻¹; 6000 mg l⁻¹;7000 mg l⁻¹; 8000 mg l⁻¹; or 9000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 10,000 mg l⁻¹ or greater. Suitably, theaqueous system has a total dissolved solids (TDS) of at least 11,000 mgl⁻¹, for example at least: 12,000 mg l⁻¹; 13,000 mg l⁻¹; 14,000 mg l³¹¹; 15,000 mg l⁻¹; 16,000 mg l⁻¹; 17,000 mg l⁻¹; 18,000 mg l⁻¹; or 19,000mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 20,000 mg l⁻¹ or greater. Suitably, theaqueous system has a total dissolved solids (TDS) of at least 21,000 mgl⁻¹, for example at least: 22,000 mg l⁻¹; 23,000 mg l⁻¹; 24,000 mg l⁻¹;25,000 mg l⁻¹; 26,000 mg l⁻¹; 27,000 mg l⁻¹; 28,000 mg l⁻¹; or 29,000 mgl⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 30,000 mg l⁻¹ or greater. Suitably, theaqueous system has a total dissolved solids (TDS) of at least 31,000 mgl⁻¹, for example at least: 32,000 mg l⁻¹; for example at least: 33,000mg l⁻¹; 34,000 mg l⁻¹; 35,000 mg l⁻¹; 36,000 mg l⁻¹; 37,000 mg l⁻¹;38,000 mg l⁻¹; 39,000 mg l⁻¹; or 40,000 mg l⁻¹.

The method may comprise treating an aqueous system having a totaldissolved solids (TDS) of 50,000 mg l⁻¹ or greater. The aqueous systemmay have a total dissolved solids (TDS) of at least 60,000 mg l⁻¹, forexample at least: 70,000 mg l⁻¹; 80,000 mg l⁻¹; 90,000 mg l⁻¹; 100,000mg l⁻¹; 110,000 mg l⁻¹; 120,000 mg l⁻¹; 130,000 mg l⁻¹; 140,000 mg l⁻¹;150,000 mg l⁻¹; 160,000 mg l⁻¹; 170,000 mg l⁻¹; 180,000 mg l⁻¹; 190,000mg l⁻¹; 200,000 mg l⁻¹; 210,000 mg l⁻¹; 220,000 mg l⁻¹; 230,000 mg l⁻¹;240,000 mg l⁻¹; or 250,000 mg l⁻¹; 260,000 mg l⁻¹; 270,000 mg l⁻¹;280,000 mg l⁻¹; 290,000 mg l⁻¹; 300,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 250,000 mg l⁻¹ or less. The aqueous system mayhave a total dissolved solids (TDS) of no more than 240,000 mg l⁻¹, forexample no more than 230,000 mg l⁻¹; 220,000 mg l⁻¹; 210,000 mg l⁻¹;200,000 mg l⁻¹; 190,000 mg l⁻¹; 180,000 mg l⁻¹; 170,000 mg l⁻¹; 160,000mg l⁻¹;

150,000 mg l⁻¹; 140,000 mg l⁻¹; 130,000 mg l⁻¹; 120,000 mg l⁻¹; or110,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 100,000 mg l⁻¹ or less. The aqueous system mayhave a total dissolved solids (TDS) of no more than 90,000 mg l⁻¹, forexample no more than 80,000 mg l⁻¹; 70,000 mg l⁻¹; 60,000 mg l⁻¹; 50,000mg l⁻¹; or 40,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of at least 25,000 mg l⁻¹. Suitably, the methodcomprises treating an aqueous system having a total dissolved solids(TDS) of at least 30,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of from 10,000 mg l⁻¹ to 300,000 mg l⁻¹.Suitably, the method comprises treating an aqueous system having a totaldissolved solids (TDS) of from 10,000 mg l⁻¹ to 100,000 mg l⁻¹.Suitably, the aqueous system has a total dissolved solids (TDS) of from20,000 mg l⁻¹ to 100,000 mg l⁻¹, for example from 25,000 mg l⁻¹ to100,000 mg l⁻¹. Suitably, the aqueous system has a total dissolvedsolids (TDS) of from 30,000 mg l⁻¹ to 100,000 mg l⁻¹. Suitably, themethod comprises treating an aqueous system having a total dissolvedsolids (TDS) of from 20,000 mg l⁻¹ to 80,000 mg l⁻¹, for example from25,000 mg l⁻¹ to 80,000 mg l⁻¹. Suitably, the method comprises treatingan aqueous system having a total dissolved solids (TDS) of from 30,000mg l⁻¹ to 80,000 mg l⁻¹.

Suitably, the method comprises treating an aqueous system to inhibit thegrowth of a plurality of different micro-organisms.

Suitably, the method comprises treating an aqueous system to prevent thegrowth of one or more micro-organisms. Suitably, the method comprisestreating an aqueous system to prevent the growth of a plurality ofdifferent micro-organisms.

Suitably, the method comprises treating an aqueous system to kill one ormore micro-organisms. Suitably, the method comprises treating an aqueoussystem to kill a plurality of different micro-organisms.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of one or more micro-organisms therein and/or toreduce the number of live micro-organisms therein, wherein saidmicro-organisms are selected from bacteria, fungi and algae. Suitably,the method comprises a method of inhibiting growth of bacteria and/orkilling bacteria. Suitably, the method comprises a method of inhibitinggrowth of fungi and/or killing fungi. Suitably, the method comprises amethod of inhibiting growth of algae and/or killing algae.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of anaerobic micro-organisms. Suitably, the methodcomprises treating an aqueous system to kill anaerobic micro-organisms.Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of anaerobic bacteria. Suitably, the method comprisestreating an aqueous system to kill anaerobic bacteria. Suitably, themethod comprises treating an aqueous system to inhibit or prevent thegrowth of facultative anaerobic bacteria. Suitably, the method comprisestreating an aqueous system to kill facultative anaerobic bacteria.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of aerobic micro-organisms. Suitably, the methodcomprises treating an aqueous system to kill aerobic micro-organisms.Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of aerobic bacteria. Suitably, the method comprisestreating an aqueous system to kill aerobic bacteria.

Suitably, the method comprises treating an aqueous system to inhibit orprevent the growth of anaerobic and aerobic micro-organisms. Suitably,the method comprises treating an aqueous system to kill anaerobic andaerobic micro-organisms. Suitably, the method comprises treating anaqueous system to inhibit or prevent the growth of anaerobic and aerobicbacteria. Suitably, the method comprises treating an aqueous system tokill anaerobic and aerobic bacteria.

The method may comprise a method of inhibiting growth of gram-positiveaerobic bacteria, gram-positive facultative anaerobic bacteria,gram-negative aerobic bacteria, gram-negative facultative anaerobicbacteria, gram-positive anaerobic bacteria and/or gram-negativeanaerobic bacteria. The method may comprise a method of inhibitinggrowth of mold and/or yeast. The method may comprise a method ofinhibiting the growth of blue green algae and/or green algae. Suitably,the method comprises a method of inhibiting the growth of gram-negativeaerobic bacteria, gram-negative facultative anaerobic bacteria,gram-negative anaerobic bacteria, and green algae. Suitably, the methodcomprises inhibiting the growth of Pseudomonas aeruginosa bacteria in anaqueous system. Suitably, the method comprises inhibiting the growth ofEnterobacter aerogenes bacteria in an aqueous system. Suitably, themethod comprises inhibiting the growth of Desulfovibrio vulgarisbacteria in an aqueous system. Suitably, the method comprises inhibitingthe growth of Chlorella vulgaris algae in an aqueous system.

Suitably, the method comprises adding a phosphonium compound treatmentagent and an oxazolidine compound treatment agent to an aqueous systemsuch that a Log 10 reduction of 1 or greater in an anaerobe culture isobtained after a contact time of 24 hours. Suitably, the methodcomprises obtaining a Log 10 reduction of 2 or greater to an anaerobeculture after a contact time of 24 hours; for example of 3 or greater; 4or greater; or 5 or greater.

Suitably, the method comprises adding a phosphonium compound and anoxazolidine compound to an aqueous system such that a complete kill ofan anaerobe culture is obtained after a contact time of 24 hours.

Suitably, the method comprises adding a phosphonium compound treatmentagent and an oxazolidine compound treatment agent to an aqueous systemsuch that a Log 10 reduction of 1 or greater in an anaerobe culture isobtained after a contact time of 4 hours. Suitably, the method comprisesobtaining a Log 10 reduction of 2 or greater to an anaerobe cultureafter a contact time of 4 hours; for example of 3 or greater; 4 orgreater; or 5 or greater.

Suitably, the method comprises adding a phosphonium compound and anoxazolidine compound to an aqueous system such that a complete kill ofan anaerobe culture is obtained after a contact time of 4 hours.

Suitably, the method comprises adding a phosphonium compound treatmentagent and an oxazolidine compound treatment agent to an aqueous systemsuch that a Log 10 reduction of 1 or greater in an anaerobe culture isobtained after a contact time of 1 hour. Suitably, the method comprisesobtaining a Log 10 reduction of 2 or greater to an anaerobe cultureafter a contact time of 1 hours; for example of 3 or greater; 4 orgreater; or 5 or greater.

Suitably, the method comprises adding a phosphonium compound and anoxazolidine compound to an aqueous system such that a complete kill ofan anaerobe culture is obtained after a contact time of 1 hour.

Suitably, the method comprises adding a phosphonium compound treatmentagent and a oxazolidine compound treatment agent to an aqueous systemsuch that a Log 10 reduction of 1 or greater in a facultative anaerobeculture is obtained after a contact time of 24 hours. Suitably, themethod comprises obtaining a Log 10 reduction of 2 or greater to afacultative anaerobe culture after a contact time of 24 hours; forexample of 3 or greater; 4 or greater; or 5 or greater. Suitably, themethod comprises obtaining a Log 10 reduction of 6 or greater to afacultative anaerobe culture after a contact time of 24 hours; forexample of 7 or greater; or 8 or greater.

Suitably, the method comprises adding a phosphonium compound, and anoxazolidine compound to an aqueous system such that a complete kill of afacultative anaerobe culture is obtained after a contact time of 24hours.

Suitably, the method comprises adding a phosphonium compound treatmentagent and a oxazolidine compound treatment agent to an aqueous systemsuch that a Log 10 reduction of 1 or greater in a facultative anaerobeculture is obtained after a contact time of 4 hours. Suitably, themethod comprises obtaining a Log 10 reduction of 2 or greater to afacultative anaerobe culture after a contact time of 4 hours; forexample of 3 or greater; 4 or greater; 5 or greater; or 6 or greater.

Suitably, the method comprises adding a phosphonium compound treatmentagent and a oxazolidine compound treatment agent to an aqueous systemsuch that a Log 10 reduction of 1 or greater in a facultative anaerobeculture is obtained after a contact time of 1 hour. Suitably, the methodcomprises obtaining a Log 10 reduction of 2 or greater to a facultativeanaerobe culture after a contact time of 1 hours; for example of 3 orgreater; or 4 or greater.

The method may comprise adding a phosphonium compound treatment agentand a oxazolidine compound treatment agent to an aqueous system suchthat a Log 10 reduction of 1 or greater in an aerobe culture is obtainedafter a contact time of 24 hours. The method may comprise obtaining aLog 10 reduction of 2 or greater to an aerobe culture after a contacttime of 24 hours; for example of 3 or greater; 4 or greater; 5 orgreater; or 6 or greater.

The method may comprise adding a phosphonium compound treatment agentand a oxazolidine compound treatment agent to an aqueous system suchthat a Log 10 reduction of 1 or greater in an aerobe culture is obtainedafter a contact time of 4 hours. The method may comprise obtaining a Log10 reduction of 2 or greater to an aerobe culture after a contact timeof 4 hours; for example of 3 or greater; 4 or greater; 5 or greater; or6 or greater.

The method may comprise adding a phosphonium compound treatment agentand a oxazolidine compound treatment agent to an aqueous system suchthat a Log 10 reduction of 1 or greater in an aerobe culture is obtainedafter a contact time of 1 hour. The method may comprise obtaining a Log10 reduction of 2 or greater to an aerobe culture after a contact timeof 1 hours; for example of 3 or greater; or 4 or greater.

Suitably, the method comprises adding treatment agents to an aqueoussystem such that compound (a) and compound (b) are added to the aqueoussystem in a total amount of from 1 to 1000 parts by weight active perone million parts by weight of said aqueous system (ppm), for examplefrom 5 to 800 ppm.

As used herein, all references to ppm refer to parts per million byweight unless stated otherwise.

Suitably, the method comprises adding compound (a) and compound (b) tothe aqueous system such that they are added in a total amount of from 5to 600 ppm. Suitably, the method comprises adding compound (a) andcompound (b) to the aqueous system such that they are added in a totalamount of from 5 to 500 ppm. Suitably, the method comprises addingcompound (a) and compound (b) to the aqueous system such that they areadded in a total amount of from 10 to 400 ppm, for example 10 to 300ppm. Suitably, the method comprises adding compound (a) and compound (b)to the aqueous system such that they are added in a total amount of from10 to 200 ppm, for example 20 to 200 ppm. Suitably, the method comprisesadding compound (a) and compound (b) to the aqueous system such thatthey are added in a total amount of from 30 to 200 ppm, for example 40to 150 ppm.

Suitably, the method comprises adding a oxazolidine compound treatmentagent to an aqueous system in an amount of at least 5 parts per million(ppm).

Suitably, the method comprises adding a oxazolidine compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said oxazolidine compound in an amount of at least 1 part permillion (ppm).

The method may comprise adding an aqueous solution comprising anoxazolidine compound to an aqueous system. The method may compriseadding an aqueous solution comprising 4,4-dimethyloxazolidine to anaqueous system.

The method may comprise adding an oxazolidine composition to an aqueoussystem.

Suitably, the method comprises adding an oxazolidine compound to anaqueous system such that it is added in an amount of greater than 5 ppm.Suitably, the method comprises adding an oxazolidine compound to anaqueous system such that it is added in an amount of at least 10 ppm.Suitably, the method comprises adding an oxazolidine compound to anaqueous system such that it is added in an amount of at least: 15 ppm,for example at least: 20 ppm; 25 ppm; 30 ppm; 35 ppm or 40 ppm. Themethod may comprise adding an oxazolidine compound to an aqueous systemsuch that it is added in an amount of at least 50 ppm, for example atleast: 60 ppm; 70 ppm; 80 ppm; 90 ppm or 100 ppm.

Suitably, the method comprises adding an oxazolidine compound to anaqueous system such that it is present in an active amount of greaterthan 1 ppm. Suitably, the method comprises adding an oxazolidinecompound to an aqueous system such that it is present in an activeamount of at least 5 ppm. Suitably, the method comprises adding anoxazolidine compound to an aqueous system such that it is present in anactive amount of at least 10 ppm, for example at least: 15 ppm; 20 ppm;25 ppm; 30 ppm; 35 ppm or 40 ppm. The method may comprise adding anoxazolidine compound to an aqueous system such that it is present in anactive amount of at least 60 ppm; 70 ppm; 80 ppm; 90 ppm or 100 ppm.

Suitably, the method comprises adding an oxazolidine compound to anaqueous system such that it is added in an amount of not more than 800ppm. Suitably, the method comprises adding an oxazolidine compound to anaqueous system such that it is added in an amount of not more than 700ppm; for example not more than: 600 ppm; or 500 ppm. Suitably, themethod comprises adding an oxazolidine compound to an aqueous systemsuch that it is added in an amount of not more than 400 ppm.

Suitably, the method comprises adding an oxazolidine compound to anaqueous system such that it is present in an active amount of not morethan 500 ppm. Suitably, the method comprises adding an oxazolidinecompound to an aqueous system such that it is present in an activeamount of not more than 400 ppm, for example not more than 300 ppm.Suitably, the method comprises adding an oxazolidine compound to anaqueous system such that it is present in an active amount of not morethan 200 ppm, for example not more than 100 ppm.

Suitably, the method comprises adding an oxazolidine compound to anaqueous system to provide a treated aqueous system comprising saidoxazolidine compound in an amount of 1 to 500 ppm, for example 10 to 400ppm. The method may comprise adding an oxazolidine compound to anaqueous system to provide a treated aqueous system comprising saidoxazolidine compound in an amount of 20 to 100 ppm, for example 30 to 90ppm.

Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is added in an amount of at least 5 ppm.Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is added in an amount of at least 10 ppm.Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is added in an amount of at least: 15 ppm,for example at least: 20 ppm; 25 ppm; 30 ppm; 35 ppm or 40 ppm. Themethod may comprise adding 4,4-dimethyloxazolidine to an aqueous systemsuch that it is added in an amount of at least 50 ppm, for example atleast: 60 ppm; 70 ppm; 80 ppm; 90 ppm or 100 ppm.

Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is present in an active amount of at least 1ppm. Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is present in an active amount of at least 5ppm. Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is present in an active amount of at least10 ppm, for example at least: 15 ppm; 20 ppm; 25 ppm; 30 ppm; 35 ppm or40 ppm. The method may comprise adding 4,4-dimethyloxazolidine to anaqueous system such that it is present in an active amount of at least60 ppm; 70 ppm; 80 ppm; 90 ppm or 100 ppm.

Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is added in an amount of not more than 800ppm. Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is added in an amount of not more than 700ppm; for example not more than: 600 ppm; or 500 ppm. Suitably, themethod comprises adding 4,4-dimethyloxazolidine to an aqueous systemsuch that it is added in an amount of not more than 400 ppm.

Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system such that it is present in an active residual amount ofnot more than 500 ppm. Suitably, the method comprises adding4,4-dimethyloxazolidine to an aqueous system such that it is present inan active residual amount of not more than 400 ppm, for example not morethan 300 ppm. Suitably, the method comprises adding4,4-dimethyloxazolidine to an aqueous system such that it is present inan active residual amount of not more than 200 ppm, for example not morethan 100 ppm.

Suitably, the method comprises adding 4,4-dimethyloxazolidine to anaqueous system to provide a treated aqueous system comprising4,4-dimethyloxazolidine in an amount of 1 to 500 ppm, for example 10 to400 ppm. The method may comprise adding 4,4-dimethyloxazolidine to anaqueous system to provide a treated aqueous system comprising4,4-dimethyloxazolidine in an amount of 20 to 100 ppm, for example 30 to90 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system in an amount of at least 0.1 parts permillion (ppm).

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound in an amount of at least 0.1 partsper million (ppm).

Suitably, the method comprises adding a phosphonium compound to anaqueous system such that it is added in an amount of at least 0.2 ppm.Suitably, the method comprises adding a phosphonium compound to anaqueous system such that it is added in an amount of at least 0.3 ppm,for example at least: 0.4 ppm; 0.5 ppm; 0.6 ppm; 0.7 ppm; 0.8 ppm; 0.9ppm; or 1.0 ppm. Suitably, the method comprises adding a phosphoniumcompound to an aqueous system such that it is added in an amount of atleast 1 ppm; for example at least 1.5 ppm; 2.0 ppm; 2.5 ppm; 3.0 ppm;3.5 ppm; 4.0 ppm; 4.5 ppm; 5.0 ppm; 5.5 ppm; or 6.0 ppm. The method maycomprise adding a phosphonium compound to an aqueous system such that itis added in an amount of at least 6 ppm, for example at least: 7 ppm; 8ppm; 9 ppm; 10 ppm; 11 ppm; 12 ppm.

Suitably, the method comprises adding a phosphonium compound to anaqueous system such that it is present in an active amount of at least0.2 ppm. Suitably, the method comprises adding a phosphonium compound toan aqueous system such that it is present in an active amount of atleast 0.3 ppm, for example at least: 0.4 ppm; 0.5 ppm; 0.6 ppm; 0.7 ppm;0.8 ppm; 0.9 ppm; or 1.0 ppm. Suitably, the method comprises adding aphosphonium compound to an aqueous system such that it is present in anactive amount of at least 1 ppm; for example at least 1.5 ppm; 2.0 ppm;2.5 ppm; 3.0 ppm; 3.5 ppm; 4.0 ppm; 4.5 ppm; 5.0 ppm; 5.5 ppm; or 6.0ppm. The method may comprise adding a phosphonium compound to an aqueoussystem such that it is present in an active amount of at least 6 ppm,for example at least: 7 ppm; 8 ppm; 9 ppm; 10 ppm; 11 ppm; 12 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound added in an amount of 1 to 20 ppm,for example 1 to 15 ppm. Suitably, the method comprises adding aphosphonium compound treatment agent to an aqueous system to provide atreated aqueous system comprising said phosphonium compound added in anamount of 1 to 10 ppm, for example 2 to 8 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system in an amount of not more than 250 ppm, forexample not more than 125 ppm.

Suitably, the method may comprises adding a phosphonium compoundtreatment agent to an aqueous system in an amount of not more than 100ppm, for example not more than 50 ppm. Suitably, the method comprisesadding a phosphonium compound to an aqueous system such that it is addedin an amount of not more than 40 ppm, for example not more than 35 ppm.The method may comprise adding a phosphonium compound to an aqueoussystem such that it is added in an amount of not more than 30 ppm, forexample not more than; 25 ppm; 20 ppm; 15 ppm; 10 ppm or 5 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound in an active amount of not morethan 250 ppm, for example not more than 125 ppm.

Suitably, the method comprises adding a phosphonium compound treatmentagent to an aqueous system to provide a treated aqueous systemcomprising said phosphonium compound in an active amount of not morethan 100 ppm, for example not more than 50 ppm. Suitably, the methodcomprises adding a phosphonium compound to an aqueous system such thatit is present in an active amount of not more than 40 ppm, for examplenot more than 35 ppm. The method may comprise adding a phosphoniumcompound to an aqueous system such that it is present in an amount ofnot more than 30 ppm, for example not more than; 25 ppm; 20 ppm; 15 ppm;10 ppm; or 5 ppm.

Suitably, the method comprises adding a phosphonium compound (a) and aoxazolidine compound (b) to an aqueous system in a weight ratio,expressed as active compound, of phosphonium compound:oxazolidinecompound of from 1.0:0.5 to 1.0:100.0, for example from 1.0:1.0 to1.0:50.0.

As used herein, all ratios are weight ratios unless stated otherwise.

Suitably, the method comprises adding a phosphonium compound (a) and aoxazolidine compound (b) to an aqueous system in a weight ratio,expressed as active compound, of phosphonium compound:oxazolidinecompound of from 1.0:2.0 to 1.0:20.0, for example from 1.0:3.0 to1.0:15.0.

Suitably, the method comprises adding a phosphonium compound (a) and aoxazolidine compound (b) to an aqueous system in a weight ratio,expressed as active compound, of phosphonium compound:oxazolidinecompound of from 1.0:1.0 to 1.0:10.0, for example from 1.0:5.0 to1.0:8.0.

Suitably, the method comprises adding a phosphonium compound (a) and aoxazolidine compound (b) to an aqueous system in a weight ratio,expressed as active compound, of phosphonium compound:oxazolidinecompound of from 1.0:5.0 to 1.0:20.0, for example from 1.0:11.0 to1.0:15.0.

The method may comprise adding a phosphonium compound (a) and aoxazolidine compound (b) to an aqueous system to provide a treatedaqueous system comprising said phosphonium compound (a) and saidoxazolidine compound (b) in a weight ratio, expressed as activecompound, of phosphonium compound:oxazolidine containing compound of atleast 1.0:100.0, for example at least 1.0:50.0.

Suitably the method comprises adding a phosphonium compound (a) and aoxazolidine compound (b) to an aqueous system to provide a treatedaqueous system comprising said phosphonium compound (a) and saidoxazolidine compound (b) in a weight ratio, expressed as activecompound, of phosphonium compound:oxazolidine compound of at least1.0:20.0, for example of at least: 1.0:15.0.

Suitably the method comprises adding a phosphonium compound (a) and aoxazolidine compound (b) to an aqueous system to provide a treatedaqueous system comprising said phosphonium compound (a) and saidoxazolidine compound (b) in a weight ratio, expressed as activecompound, of phosphonium compound:oxazolidine containing compound of nogreater than 1.0:0.5, for example no greater than 1.0:1.0.

The method may comprise adding a phosphonium compound (a) and aoxazolidine compound (b) to an aqueous system to provide a treatedaqueous system comprising said phosphonium compound (a) and saidoxazolidine compound (b) in a weight ratio, expressed as activecompound, of phosphonium compound:oxazolidine containing compound of nogreater than 1.0:2.0, for example no greater than 1.0:5.0.

The method may comprise adding a combination of phosphonium compounds(a) to an aqueous system. Suitably, the method comprises adding a singletype of phosphonium compound (a) to an aqueous system.

Suitably, the method employs a phosphonium compound (a) having formula:

wherein each R is independently a C₁-C₆ alkyl group which isunsubstituted or substituted by a cyano, hydroxyl, esterified hydroxylor aryl group;

-   -   R¹ represents a C₈-C₁₈ alkyl group which is substituted or        unsubstituted; and

X represents either chlorine or bromine.

Suitably, each R is a C₁-C₆ alkyl group. Suitably, each R is a C₃-C₅alkyl group. Suitably each R is a butyl group.

Suitably R¹ represents a C₈-C₁₈ alkyl group. Suitably, R1 is a C₁₂-C₁₆alkyl group. Suitably, R¹ is a tetradecyl group.

Suitably, X is chlorine.

Suitably, the method employs a phosphonium compound (a) which is aphosphonium chloride.

Suitably, the method comprises treating an aqueous system such thatphosphonium chloride comprises greater than 50% of the total phosphoniumcompound(s) added to the aqueous system. Suitably, the method comprisestreating an aqueous system such that phosphonium chloride comprisesgreater than 90% of the total phosphonium compound(s) added to theaqueous system, for example 99% or greater.

Suitably, the method comprises treating an aqueous system such thatphosphonium chloride comprises greater than 50% of the total phosphoniumcompound(s) present in the aqueous system. Suitably, the methodcomprises treating an aqueous system such that phosphonium chloridecomprises greater than 90% of the total phosphonium compound(s) presentin the aqueous system, for example 99% or greater.

Suitably, the method employs a phosphonium chloride as the onlyphosphonium compound (a).

Suitably, the method comprises adding tri n-butyl n-tetradecylphosphonium chloride (hereafter “TTPC”) to the aqueous system. Suitably,the phosphonium compound (a) comprises TTPC. Suitably, the phosphoniumcompound (a) consists of TTPC.

Suitably, the method comprises adding an aqueous composition containingthe phosphonium compound (a) to the aqueous system. Suitably, the methodcomprises adding an aqueous composition of TTPC to the aqueous system.The method may comprise adding an aqueous composition comprising 5% byweight of TTPC to the aqueous system. A suitable composition containingTTPC is available from BWA Water Additives and is sold under the tradename Bellacide 355 (an aqueous composition of TTPC and water consistingof water and 5% by weight of TTPC). The method may comprise adding anaqueous composition comprising 50% by weight of TTPC to the aqueoussystem. A suitable composition containing TTPC is available from BWAWater Additives and is sold under the trade name Bellacide 350 (anaqueous composition of TTPC and water consisting of water and 50% byweight of TTPC).

Suitably, the method comprises treating an aqueous system such that TTPCcomprises greater than 50% of the total phosphonium compound(s) added tothe aqueous system. Suitably, the method comprises treating an aqueoussystem such that TTPC comprises greater than 90% of the totalphosphonium compound(s) added to the aqueous system, for example 99% orgreater.

Suitably, the method comprises treating an aqueous system such that TTPCcomprises greater than 50% of the total phosphonium compound(s) presentin the aqueous system. Suitably, the method comprises treating anaqueous system such that TTPC comprises greater than 90% of the totalphosphonium compound(s) present in the aqueous system, for example 99%or greater.

Suitably, the method employs TTPC as the only phosphonium compound (a).

The method may employ a synergistic mixture of compound (a) and compound(b). Suitably, by “synergistic mixture” it is meant that the mixture ofcompounds (a) and compound (b) has a synergistic effect on theinhibition of growth of one or more biological organisms, preferablymicro-organisms such as bacteria, fungi and/or algae and/or has asynergistic effect on reducing the number of one or more biologicalorganisms, preferably micro-organisms such as bacteria, fungi and/oralgae.

The method may comprise adding compound (a) and compound (b) to theaqueous system such that the aqueous system comprises a synergisticmixture of compound (a) and compound (b).

The method may comprise adding compound (a) and compound (b) as amixture to the aqueous system. The method may comprise adding compound(a) and compound (b) separately to the aqueous system and allowing orcausing them to mix within the aqueous system.

Where the method comprises mixing compound (a) and compound (b) andadding the mixture to the aqueous system and/or adding compound (a) andcompound (b) separately to the aqueous system and allowing or causingthem to mix within the aqueous system then compound (a) and compound (b)are suitably used in the form of aqueous compositions.

Suitably, compound (a) is used in the form of an aqueous compositioncomprising between 1% and 90% by weight of compound (a), for examplebetween 1% and 60% by weight. Suitably, compound (a) is used in the formof an aqueous composition comprising between 1% and 10% by weight ofcompound (a), for example 5% by weight.

Suitably, compound (b) is used in the form of an aqueous compositioncomprising between 10% and 90% by weight of compound (b), for examplebetween 50% and 80%. Suitably, compound (b) is used in the form of anaqueous composition comprising between 70% and 80% by weight of compound(b), for example between 70% and 75%.

The method may comprise a method of treating an industrial water system.The method may comprise treating a cooling water system. The method maycomprise treating a pulping and/or papermaking water system. The methodmay comprise treating an oil and/or gas field water system. The methodmay comprise treating an aqueous system to control the growth ofbacterial and/or algal micro-organisms contained therein and/or whichmay become entrained in said system.

It has been found that the compositions and methods of utilisation ofthe present invention may in particular be efficacious in controllingacid producing facultative anaerobic bacteria and hydrogen sulphideproducing anaerobic bacteria which may populate aqueous systems.

Surprisingly, it has been found that when compound (a) and compound (b)are combined the resulting combination may pose a higher degree ofbiocidal activity in an aqueous system than that of the individualcompounds used alone. Because of the enhanced activity of thecombination of treatment agent compounds, it may be possible for thetotal quantity of treatment agent added to an aqueous system to bereduced in comparison to a system using only one of said treatment agentcompounds. In addition, the high degree of biocidal activity which isprovided by each of the treatment agent compounds may be exploitedwithout use of higher concentrations of each. The combination of TTPCand 4,4-dimethyloxazolidine may be particularly effective. Thecomposition may also be surprisingly effective in systems having hightotal dissolved solids (TDS).

It has been found that the compositions and methods of utilisation ofthe present invention may in particular be efficacious in controllingthe facultative anaerobic bacterium Enterobacter aerogenes and/or theanaerobic bacterium Desulfovibrio vulgaris, which may populate aqueoussystems.

Surprisingly, the present inventor has found that mixtures of compound(a) and compound (b) such as mixtures of tri-n-butyl n-tetradecylphosphonium chloride (TTPC) and 4,4-dimethyloxazolidine are especiallyefficacious in controlling the growth of micro-organisms such asbacterial and algal microbes in aqueous systems comprising dissolvedsolids and there is an unexpected synergistic relationship.

It has been found that compositions of compounds (a) and compound (b)may be unexpectedly effective against facultative anaerobes andanaerobes and may have a marked synergy in relation to anaerobes atshort contact times. For example, 4,4-dimethyloxazolidine may have somebiocidal activity against anaerobes at short contact times but theaddition of TTPC may greatly improve performance even though TTPC alonemay be ineffective against anaerobes at short contact times

According to a second aspect of the present invention there is provideda method of treating an aqueous system to inhibit growth of one or moremicro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to said aqueous system and wherein said treatment agentscomprise:

(i) tri n-butyl n-tetradecyl phosphonium chloride (TTPC); and(ii) 4,4-dimethyloxazolidine (DMO).

Suitably, the aqueous system comprises dissolved solids.

Suitably, the aqueous system comprises greater than 10,000 mg l⁻¹ totaldissolved solids (TDS). The aqueous system may comprise greater than20,000 mg l⁻¹ TDS, for example greater than 30,000 mg l⁻¹ TDS.

The method of the second aspect may comprise any feature as described inrelation to the first aspect except where such features are mutuallyexclusive.

According to a third aspect of the present invention there is providedan aqueous system comprising a combination of:

(a) a phosphonium compound; and(b) an oxazolidine compound.

Suitably, the aqueous system comprises dissolved solids.

Suitably, the aqueous system comprises greater than 10,000 mg l⁻¹ totaldissolved solids (TDS). The aqueous system may comprise greater than20,000 mg l⁻¹ TDS, for example greater than 30,000 mg l⁻¹ TDS.

Suitably, the phosphonium compound (a) has formula:

wherein each R is independently a C₁-C₆ alkyl group which isunsubstituted or substituted by a cyano, hydroxyl, esterified hydroxylor aryl group;

-   -   R¹ represents a C₈-C₁₈ alkyl group which is substituted or        unsubstituted; and

X represents either chlorine or bromine.

Suitably, each R is a C₁-C₆ alkyl group. Suitably, each R is a C₃-C₅alkyl group. Suitably each R is a butyl group.

Suitably R¹ represents a C₈-C₁₈ alkyl group. Suitably, R1 is a C₁₂-C₁₆alkyl group. Suitably, R¹ is a tetradecyl group.

Suitably, X is chlorine.

Suitably, the phosphonium compound (a) is a phosphonium chloride.

Suitably, said compound (a) comprises TTPC.

Suitably, the oxazolidine compound (b) comprise a methyloxazolidine.Suitably, the oxazolidine compound (b) comprise a dimethyloxazolidine.

Suitably, said compound (b) comprises 4,4-dimethyloxazolidine.

Suitably the aqueous system comprises a mixture of water and otherconstituents. The aqueous system may contain oil. The aqueous system maycomprise an oil and water emulsion. The aqueous system may comprisesolids. The aqueous system may comprise suspended solids. The aqueoussystem may comprise high levels of dissolved solids. The aqueous systemmay comprise one or more salts, for example sodium chloride. Suitably,the aqueous system consists of a body of water. Suitably, the aqueoussystem consists of a body of water which comprises water and otherconstituents, for example dissolved solids.

Suitably, the aqueous system comprises an industrial water system. Theaqueous system may consist of industrial water. The aqueous system maycomprise a cooling water system. The aqueous system may comprise apulping and papermaking system. The aqueous system may comprise an oiland gas field water system. The aqueous system may comprise a welltreatment fluid.

The aqueous system may comprise cooling water. The aqueous system mayconsist of cooling water, comprising compound (a), compound (b) andoptionally other constituents in addition to water. The aqueous systemmay comprise pulping and papermaking water. The aqueous system mayconsist of pulping and papermaking water, comprising compound (a),compound (b) and optionally other constituents in addition to water. Theaqueous system may comprise oil and gas field water. The aqueous systemmay consist of oil and gas field water, comprising compound (a),compound (b) and optionally other constituents in addition to water. Theaqueous system may comprise well treatment fluid. The aqueous system mayconsist of well treatment fluid, comprising compound (a), compound (b)and optionally other constituents in addition to water.

The aqueous system of the third aspect may comprise any feature asdescribed in relation to one or more of the first and/or second aspectsexcept where such features are mutually exclusive.

According to a fourth aspect of the present invention there is provideda method of inhibiting or preventing the growth of one or moremicro-organisms in a water based liquid, wherein the method comprisesadding treatment agents to said water based liquid and wherein saidtreatment agents comprise:

(a) a phosphonium compound; and(b) a oxazolidine compound.

The water based liquid may consist of water. Suitably, the water basedliquid comprises water and other constituents.

Suitably, the water based liquid comprises dissolved solids.

Suitably, the water based liquid is an aqueous media comprising waterand other constituents. Suitably, the water based liquid is an aqueousmedia comprising water and dissolved solids.

Suitably, there is provided a method of inhibiting or preventing thegrowth of one or more micro-organisms in an aqueous media, wherein themethod comprises adding treatment agents to an aqueous media comprisingdissolved solids and wherein said treatment agents comprise:

(a) a phosphonium compound; and(b) a oxazolidine compound.

Suitably, the water based liquid comprises greater than 10,000 mg l⁻¹total dissolved solids (TDS). The aqueous system may comprise greaterthan 20,000 mg l⁻¹ TDS, for example greater than 30,000 mg l⁻¹ TDS.

Suitably, the phosphonium compound (a) has formula:

wherein each R is independently a C₁-C₆ alkyl group which isunsubstituted or substituted by a cyano, hydroxyl, esterified hydroxylor aryl group;

-   -   R¹ represents a C₈-C₁₈ alkyl group which is substituted or        unsubstituted; and

X represents either chlorine or bromine.

Suitably, each R is a C₁-C₆ alkyl group. Suitably, each R is a C₃-C₅alkyl group. Suitably each R is a butyl group.

Suitably R¹ represents a C₈-C₁₈ alkyl group. Suitably, R1 is a C₁₂-C₁₆alkyl group. Suitably, R¹ is a tetradecyl group.

Suitably, X is chlorine.

Suitably, the phosphonium compound (a) is a phosphonium chloride.

Suitably, said compound (a) comprises TTPC.

Suitably, the oxazolidine compound (b) comprise a methyloxazolidine.Suitably, the oxazolidine compound (b) comprise a dimethyloxazolidine.

Suitably, said compound (b) comprises 4,4-dimethyloxazolidine.

Suitably the water based liquid comprises a mixture of water and otherconstituents. The water based liquid may contain oil. The water basedliquid may comprise an oil and water emulsion. The water based liquidmay comprise solids. The water based liquid may comprise suspendedsolids. The water based liquid may comprise high levels of dissolvedsolids. The water based liquid may comprise one or more salts, forexample sodium chloride.

The water based liquid may comprise industrial water. The water basedliquid may consist of industrial water which may comprise water andother constituents. The water based liquid may comprise cooling water.The water based liquid may consist of cooling water which may comprisewater and other constituents. The water based liquid may comprisepulping and papermaking water. The water based liquid may consist ofpulping and papermaking water which may comprise water and otherconstituents. The water based liquid may comprise oil and gas fieldwater. The water based liquid may consist of oil and gas field waterwhich may comprise water and other constituents. The water based liquidmay comprise a well treatment fluid. The water based liquid may consistof well treatment fluid which may comprise water and other constituents.

Suitably, the method comprises treating industrial water to inhibitgrowth of one or more micro-organisms therein and/or to reduce thenumber of live micro-organisms therein. The method may comprise treatingcooling water to inhibit growth of one or more micro-organisms thereinand/or to reduce the number of live micro-organisms therein. The methodmay comprise treating pulping and papermaking water to inhibit growth ofone or more micro-organisms therein and/or to reduce the number of livemicro-organisms therein. The method may comprise treating oil and gasfield water to inhibit growth of one or more micro-organisms thereinand/or to reduce the number of live micro-organisms therein. The methodmay comprise treating a well treatment fluid to inhibit growth of one ormore micro-organisms therein and/or to reduce the number of livemicro-organisms therein.

The method of the fourth aspect may comprise any feature as described inrelation to one or more of the first and/or second and/or third aspectsexcept where such features are mutually exclusive.

According to a fifth aspect of the present invention there is provided awater based liquid comprising dissolved solids and comprising acombination of:

(a) a phosphonium compound; and(b) an oxazolidine compound.

Suitably, the water based liquid is an aqueous media comprising waterand other constituents. Suitably, the water based liquid is an aqueousmedia comprising water and dissolved solids.

Suitably, there is provided an aqueous media comprising dissolved solidsand comprising a combination of:

(a) a phosphonium compound; and(b) a oxazolidine compound.

Suitably, the water based liquid comprises greater than 10,000 mg l⁻¹total dissolved solids (TDS). The aqueous system may comprise greaterthan 20,000 mg l⁻¹ TDS, for example greater than 30,000 mg l⁻¹ TDS.

Suitably, the phosphonium compound (a) has formula:

wherein each R is independently a C₁-C₆ alkyl group which isunsubstituted or substituted by a cyano, hydroxyl, esterified hydroxylor aryl group;

-   -   R¹ represents a C₈-C₁₈ alkyl group which is substituted or        unsubstituted; and

X represents either chlorine or bromine.

Suitably, each R is a C₁-C₆ alkyl group. Suitably, each R is a C₃-C₅alkyl group. Suitably each R is a butyl group.

Suitably R¹ represents a C₈-C₁₈ alkyl group. Suitably, R1 is a C₁₂-C₁₆alkyl group. Suitably, R¹ is a tetradecyl group.

Suitably, X is chlorine.

Suitably, the phosphonium compound (a) is a phosphonium chloride.

Suitably, said compound (a) comprises TTPC.

Suitably, the oxazolidine compound (b) comprise a methyloxazolidine.Suitably, the oxazolidine compound (b) comprise a dimethyloxazolidine.

Suitably, said compound (b) comprises 4,4-dimethyloxazolidine.

Suitably the water based liquid comprises a mixture of water and otherconstituents. The water based liquid may contain oil. The water basedliquid may comprise an oil and water emulsion. The water based liquidmay comprise solids. The water based liquid may comprise suspendedsolids. The water based liquid may comprise high levels of dissolvedsolids. The water based liquid may comprise one or more salts, forexample sodium chloride.

The water based liquid may comprise industrial water. The water basedliquid may consist of industrial water, comprising compound (a),compound (b) and optionally other constituents in addition to water. Thewater based liquid may comprise cooling water. The water based liquidmay consist of cooling water, comprising compound (a), compound (b) andoptionally other constituents in addition to water. The water basedliquid may comprise pulping and papermaking water. The water basedliquid may consist of pulping and papermaking water, comprising compound(a), compound (b) and optionally other constituents in addition towater. The water based liquid may comprise oil and gas field water. Thewater based liquid may comprise oil and gas field water. The water basedliquid may consist of oil and gas field water, comprising compound (a),compound (b) and optionally other constituents in addition to water. Thewater based liquid may comprise a well treatment fluid. The water basedliquid may consist of well treatment fluid, comprising compound (a),compound (b) and optionally other constituents in addition to water.

The water based liquid of the fifth aspect may comprise any feature asdescribed in relation to one or more of the first and/or second and/orthird and/or fourth aspects except where such features are mutuallyexclusive.

According to a sixth aspect of the present invention there is provided abiocidal composition comprising a combination of:

(a) a phosphonium compound; and(b) an oxazolidine compound.

Suitably, the biocidal composition comprises an aqueous composition.

The biocidal composition may comprise a combination of phosphoniumcompounds (a). Suitably, the biocide comprises a single type ofphosphonium compound (a).

Suitably, the biocidal composition comprises one or more phosphoniumcompound(s), one or more oxazolidine compound(s) and water in a combinedamount of at least 50% by weight of the biocidal composition. Suitably,the biocidal composition comprises one or more phosphonium compound(s),one or more oxazolidine compound(s) and water in a combined amount of atleast 90% by weight of the biocidal composition. Suitably, the biocidalcomposition comprises one or more phosphonium compound(s), one or moreoxazolidine compound(s) and water in a combined amount of at least 95%by weight of the biocidal composition, for example at least 99% byweight. Suitably, the biocidal composition consists of one or morephosphonium compound(s), one or more oxazolidine compound(s) and water.

Suitably, the biocidal composition comprises a phosphonium compound inan amount of at least 1% by weight. The biocidal composition maycomprise a phosphonium compound in an amount of at least 2% by weight,for example at least: 3%; 4% or 5% by weight.

Suitably, the biocidal composition comprises am oxazolidine compound inan amount of at least 1% by weight. The biocidal composition maycomprise an oxazolidine compound in an amount of at least 2% by weight,for example at least: 3%; 4% or 5% by weight. The biocidal compositionmay comprise an oxazolidine compound in an amount of at least 10% byweight, for example at least: 15%; 20%; 25% or 30% by weight. Thebiocidal composition may comprise an oxazolidine compound in an amountof at least 35% by weight, for example at least: 40%; 45%; 50%; 55%;60%; 65% or 70% by weight.

Suitably, the biocidal composition comprises a phosphonium compound (a)and a oxazolidine compound (b) in a weight ratio, expressed as activecompound, of phosphonium compound:oxazolidine compound of from 1.0:0.5to 1.0:100.0, for example from 1.0:1.0 to 1.0:50.0.

Suitably, the biocidal composition comprises a phosphonium compound (a)and a oxazolidine compound (b) in a weight ratio, expressed as activecompound, of phosphonium compound:oxazolidine compound of from 1.0:2.0to 1.0:20.0, for example from 1.0:3.0 to 1.0:15.0.

Suitably, the phosphonium compound (a) has formula:

wherein each R is independently a C₁-C₆ alkyl group which isunsubstituted or substituted by a cyano, hydroxyl, esterified hydroxylor aryl group;

-   -   R¹ represents a C₈-C₁₈ alkyl group which is substituted or        unsubstituted; and

X represents either chlorine or bromine.

Suitably, each R is a C₁-C₆ alkyl group. Suitably, each R is a C₃-C₅alkyl group. Suitably each R is a butyl group.

Suitably R¹ represents a C₈-C₁₈ alkyl group. Suitably, R1 is a C₁₂-C₁₆alkyl group. Suitably, R¹ is a tetradecyl group.

Suitably, X is chlorine.

Suitably, the phosphonium compound (a) is a phosphonium chloride.

Suitably, said compound (a) comprises TTPC.

The biocidal composition may comprise a combination of oxazolidinecompounds (b). Suitably, the biocidal composition comprises a singletype of oxazolidine compounds (b).

Suitably, the oxazolidine compound (b) is selected from the groupconsisting of oxazolidines and oxazolidine derivatives. Suitably, theoxazolidine compound (b) comprises an oxazolidine. Suitably, theoxazolidine compound (b) consists of an oxazolidine. Suitably, theoxazolidine compound (b) comprises an oxazolidine derivative. Suitably,the oxazolidine compound (b) consists of an oxazolidine derivative.

Suitably, the oxazolidine compound (b) comprises a methyloxazolidine.Suitably, the oxazolidine compound (b) consists of a methyloxazolidine.Suitably, the oxazolidine compound (b) comprises a dimethyloxazolidine.Suitably, the oxazolidine compound (b) consists of adimethyloxazolidine.

Suitably, the oxazolidine compound (b) comprises4,4-dimethyloxazolidine. Suitably, the oxazolidine compound (b) consistsof 4,4-dimethyloxazolidine.

Suitably, TTPC comprises greater than 50% of the total phosphoniumcompound(s) in the biocidal composition. Suitably, TTPC comprisesgreater than 90% of the total phosphonium compound(s) in the biocidalcomposition, for example 99% or greater.

Suitably, 4,4-dimethyloxazolidine comprises greater than 50% of thetotal oxazolidine compound(s) in the biocidal composition. Suitably,4,4-dimethyloxazolidine comprises greater than 90% of the totaloxazolidine compound(s) in the biocidal composition, for example 99% orgreater.

Suitably, there is provided a biocidal composition comprising acombination of:

(a) tri n-butyl n-tetradecyl phosphonium chloride (TTPC); and(b) 4,4-dimethyloxazolidine (DMO).

The biocidal composition of the sixth aspect may comprise any feature asdescribed in relation to one or more of the first and/or second and/orthird and/or fourth and/or fifth aspects except where such features aremutually exclusive.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be illustrated by way of example withreference to the following preferred embodiments.

EXAMPLES

Aqueous systems inoculated with anaerobe and facultative anaerobeculture and having a total dissolved solids (TDS) concentration of30,000 mg l⁻¹ were prepared and treated with treatment agentscomprising: (a) a phosphonium compound and (b) an oxazolidine compound.The phosphonium compound (a) used was tri n-butyl n-tetradecylphosphonium chloride (TTPC). The oxazolidine compound (b) was4,4-dimethyloxazolidine (DMO).

TTPC was used in the form of Bellacide 350, an aqueous composition ofTTPC and water consisting of water and 50% by weight of TTPC availablefrom BWA Water Additives.

DMO was used in the form of Mergal 192 a 73.7% aqueous solution of DMOavailable from Troy Chemical Corporation.

A suspension of Desulfovibrio vulgaris plus Enterobacter aerogenesbacteria containing from 1×10⁵ to 1×10⁶ cells/mL was prepared in sterilepH 8 phosphate buffer containing sodium chloride to give the desiredtotal dissolved solids (TDS) concentration. Aliquots of this suspensionwere dosed with the indicated concentrations of the compounds (a) and(b) with the concentrations being measured as ppm active. The mixtureswere allowed to stand at room temperature. At the designated contacttimes, each mixture was sampled to determine the total number of viablecells of both Desulfovibrio vulgaris and Enterobacter aerogenes byserial 10-fold dilution into API RP 38 media vials and anaerobic acidproducing media vials, respectively. The vials were incubated at 37° C.for 72 hours. Results were recorded as log₁₀ reduction in the viablecount versus the control.

The efficacy of the treatment agents was evaluated by measuring theLog₁₀ Reduction of the anaerobic bacterium Desulfovibrio vulgaris andthe facultative anaerobic bacterium Enterobacter aerogenes after contacttimes of 1 hour, 4 hours and 24 hours as detailed in Table 1. For TTPCthe stated ppm value relates to the amount of TTPC added (active). Forthe 4,4-dimethyloxazolidine the stated ppm relates to the amount of4,4-dimethyloxazolidine added (active).

TABLE 1 Treatment Log₁₀ Contact agent Log₁₀ Reduction Ex- TDS time (ppmactive) Reduction Facultative ample (mg l⁻¹) (hours) TTPC DMO Anaerobes*Anaerobes* 1 30,000 1 3.125 — 1 1 2 30,000 1 6.25 — 2 3 3 30,000 1 — 401 0 4 30,000 1 — 80 1 0 5 30,000 1 3.125 40 5 2 6 30,000 1 6.25 40 5 4 730,000 4 3.125 — 5 2 8 30,000 4 6.25 — 5 4 9 30,000 4 — 40 1 0 10 30,0004 — 80 2 0 11 30,000 4 3.125 40 5 2 12 30,000 4 6.25 40 5 6 13 30,000 243.125 — 5 4 14 30,000 24 6.25 — 5 5 15 30,000 24 — 40 1 0 16 30,000 24 —80 2 0 17 30,000 24 3.125 40 5 8 18 30,000 24 6.25 40 5 8 *5 = completekill for anaerobes *8 = complete kill for facultative anaerobes

The results show that surprisingly, despite TTPC and DMO each beingrelatively ineffective alone against anaerobes at short contact times,the combination of TTPC and DMO was very effective against anaerobesachieving complete kill (5 log reduction) at one hour compared to a 1-2log reduction at the same concentrations of TTPC or DMO when usedindividually.

The results with facultative anaerobes, also show unexpected efficacy ofthe combination of TTPC and DMO with the combination achieving completekill (8 log reduction) at 24 hours.

Accordingly, it will be appreciated that combining TTPC and DMO mayallow for less DMO or TTPC to be used to achieve kill of facultativeanaerobes and anaerobes compared to TTPC or DMO alone. It will also beappreciated that combining TTPC and DMO may allow for complete kill offacultative anaerobes and anaerobes using TTPC and DMO at certaincontact times which may not be achievable if using only DMO or TTPC.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. A method of treating an aqueous system to inhibit growth of one ormore micro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to said aqueous system and wherein said treatment agentscomprise: (a) a tetra alkyl phosphonium compound; and (b) an oxazolidinecompound.
 2. A method according to claim 1, wherein the tetra alkylphosphonium compound (a) comprises tri n-butyl n-tetradecyl phosphoniumchloride (TTPC).
 3. A method according to claim 1, wherein theoxazolidine compound (b) comprises 4,4-dimethyloxazolidine (DMO).
 4. Amethod according to claim 1, wherein the method comprises treating anaqueous system to inhibit growth of facultative anaerobic bacteriaand/or anaerobic bacteria and/or to reduce the number of livefacultative anaerobic bacteria and/or anaerobic bacteria therein.
 5. Amethod according to claim 1, wherein the method comprises treating anaqueous system having a total dissolved solids (TDS) of 1000 mg l⁻¹ orgreater.
 6. A method according to claim 1, wherein the method comprisesadding a tetra alkyl phosphonium compound (a) to an aqueous system in anamount of at least 1 part per million (ppm).
 7. A method according toclaim 1, wherein the method comprises adding an oxazolidine compound (b)to an aqueous system such in an amount of at least at least 1 part permillion (ppm).
 8. A method according to claim 1, wherein the methodcomprises adding a tetra alkyl phosphonium compound (a) and anoxazolidine compound (b) to an aqueous system in a weight ratio,expressed as active compound, of tetra alkyl phosphoniumcompound:oxazolidine compound of from 1.0:1.0 to 1.0:50.0.
 9. A methodof treating an aqueous system to inhibit growth of one or moremicro-organisms therein and/or to reduce the number of livemicro-organisms therein, wherein the method comprises adding treatmentagents to said aqueous system and wherein said treatment agentscomprise: (i) tri n-butyl n-tetradecyl phosphonium chloride (TTPC); and(ii) 4,4-dimethyloxazolidine (DMO).
 10. A method according to claim 9,wherein the method comprises treating an aqueous system having a totaldissolved solids (TDS) of 1000 mg l⁻¹ or greater and wherein the methodcomprises adding TTPC to an aqueous system in an amount of at least 1part per million (ppm) and adding 4,4-dimethyloxazolidine to an aqueoussystem in an amount of at least 1 part per million (ppm).
 11. A methodaccording to claim 10, wherein the method comprises treating an aqueoussystem to inhibit growth of facultative anaerobic bacteria and/oranaerobic bacteria and/or to reduce the number of live facultativeanaerobic bacteria and/or anaerobic bacteria therein.
 12. An aqueoussystem incorporating a combination of: (a) a phosphonium compound; and(b) an oxazolidine compound.
 13. An aqueous system according to claim12, wherein compound (a) comprises tri n-butyl n-tetradecyl phosphoniumchloride (TTPC) and compound (b) comprises 4,4-dimethyloxazolidine(DMO).
 14. A method of inhibiting or preventing the growth of one ormore micro-organisms in a water based liquid, wherein the methodcomprises adding treatment agents to a water based liquid and whereinsaid treatment agents comprise: (a) a phosphonium compound; and (b) anoxazolidine compound.
 15. A method according to claim 14, wherein thewater based liquid comprises dissolved solids and wherein compound (a)comprises tri n-butyl n-tetradecyl phosphonium chloride (TTPC) andcompound (b) comprises 4,4-dimethyloxazolidine (DMO).
 16. An water basedliquid comprising dissolved solids and incorporating a combination of:(a) a phosphonium compound; and (b) an oxazolidine compound.
 17. Anwater based liquid according to claim 16, wherein compound (a) comprisestri n-butyl n-tetradecyl phosphonium chloride (TTPC), compound (b)comprises 4,4-dimethyloxazolidine and wherein the water based liquidcomprises greater than 10,000 mg l-1 total dissolved solids (TDS).
 18. Abiocidal composition comprising a combination of: (a) a phosphoniumcompound; and (b) an oxazolidine compound.
 19. A biocidal compositionaccording to claim 18 wherein compound (a) comprises tri n-butyln-tetradecyl phosphonium chloride (TTPC).
 20. A biocidal compositionaccording to claim 18 wherein compound (b) comprises4,4-dimethyloxazolidine (DMO).
 21. A method according to claim 1,wherein the method employs a tetra alkyl phosphonium compound (a) havingformula:

wherein each R is independently a C₁-C₆ alkyl group; R¹ represents aC₈-C₁₈ alkyl group; and X represents either chlorine or bromine.
 22. Amethod according to claim 1, wherein the method employs a tetra alkylphosphonium compound (a) having formula:

wherein each R is independently a C₃-C₅ alkyl group; R¹ represents aC₁₂-C₁₆ alkyl group; and X represents either chlorine or bromine.